In a commonly encountered form of turret mill, a depth stop is provided by a pair of locking nuts which are screw-threaded onto a vertical rod. A component (usually a ring known as a "doughnut") is arranged to move axially of the rod above the locking nuts as the tool head moves up and down, so that when the doughnut encounters the locking nuts the downward movement of the doughnut, and hence of the tool head, is thereby limited. The limit of the downward movement is adjustable by first slackening the nuts, screwing them to a new position along the rod, and then re-tightening them.
In some uses of the turret mill it is necessary to carry out different operations which require the depth stop to be positioned at different heights. The sequence of operations may be repeated many times. It is thus necessary to reset the depth stops between operations, which is time-consuming and tedious. This problem has become more acute because a system has recently become available which enables tools to be changed quickly and easily, but the time required to re-adjust the depth stop accounts for a major part of the delay between tool changes.
An aim of the present invention may be viewed as being to provide an arrangement which greatly reduces the time required to change the stop position.